GCC Mercury Laser Pro 25W Lens

[Jose Quinones]

I am looking to purchase a lens for my mercury gcc / laserpro 25W engraver. I know about laserresearch dot net but am looking to buy one of those Chinese units from ebay. Anybody with a similar laser acquired one of these lenses? I will be manufacturing the lens holder out of aluminum on a CNC mill, so this is not much of an issue. I also know the lens is 19 mm in diameter and I believe the focal length to be 2". While looking at the laser lands store on ebay I see a lot of different options and terminology I really do not recognize (CVD, ZnSe, etc). I think that if I choose a 19.05 mm diameter and 2 or 2.5" FL, I should be fine. Any other detail I should be mindful of? Thanks for any input you may provide!

[Dan Hintz]

ZnSe (Zinc Selenide) is the lens material... this is what you want for the wavelengths emitted by CO2 lasers. It has an orange-yellow color to it. 2" is a common focal length. 2.5" is a little less common with Western machines, more common with Chinese... you'll get a little more depth of focus in trade for a little less definition compared to the 2". I run 2" for (almost) everything. If you're making the holder, the diameter doesn't much matter, but roughly 0.8" (20mm) is what you should expect.

[Dave Sheldrake]

CdTe = Cadmium Telluride (not really applicable to hobby lasers)

ZnSe = Zinc Selenide (Best transmission rates) (CVD is the method of manufacture for the lens)(Chemical Vapour Deposition)

GaAs = Gallium Arsenide (Highest abrasion resistance)

Look for a Meniscus lens rather than a Plano Convex to keep abberations to the best possible levels.

Ask for the II-VI versions if they have them, (made by II-VI in China) they aren't quite the same quality as Western made from either II-VI USA or RMI but they are quite a bit better than the normal Chinese stuff.

Depth of field by focal length assuming a 6mm input beam

50mm Lens = 2mm DOF

100mm Lens = 7.5mm DOF

200mm Lens = 30mm DOF

Bigger DOF = bigger spot size = less power density so you would need more Laser watts to achieve the same cutting ability (cutting depth)

As Dan says, 2inch / 50mm Meniscus lens made of ZnSe will cover most bases on hobby lasers.

best wishes

Dave